1. Field of the Invention
This invention relates to phenolic resin compositions, more particularly to such resinous compositions which may be readily adapted for the manufacture of laminates useful in the field of telecommunications and electronics equipment and applicances.
2. Prior Art
The rapid technological advanced during the recent years in telecommunications and electronics has created a demand for high quality laminates which satisfy the various electrical and physical property requirements including dielectric constant, flexibility, chemicals resistance, dimensional stability and cold punching workability.
It has heretofore been proposed to this end therefore to provide flexible phenolic resins by for instance adding a thermoplastic polymer or a plasticizer to a phenolic resin, or by using long-chain hydrocarbon substituted phenol derivatives as the starting material, or by blending the resin with rubber. These alternatives have however proven to be unsatisfactory in their performance.
It has also been proposed to provide phenolic resins eligible for laminates by reacting phenols with drying oils or liquid diolefin polymers in the presence of acid catalysts and subsequently with formaldehyde. This proposal has a drawback in that phenols can be added only slowly to such drying oils or liquid diolefin polymers that have non-conjugated double bonds, coupled with these double bonds becoming cyclized or polymerized. Increased phenols added to drying oils or liquid diolefin polymers would lead to such side reactions and the resulting composition is difficult to dissolve in a polar solvent when making a varnish, or sparingly compatible with phenolic resins, or hardly permeable to paper or cloth.
Phenolic resins modified by a drying oil having conjugated double bonds such as tung oil are relatively free from the above drawbacks and capable of retaining adequate flexibility.
However, tung oil is a natural product and its price is very unstable. Moreover, the performance of tung oil modified phenolic resins has been insufficient for the modern electrical equipment and appliances which have been rapidly advancing. Therefore, new reactive plasticizers are demanded.